Analysis Of Internal Flow Characteristics In A Centrifugal Pump At Low Flow Rates

With the development of society and science technology, people pay more attention to the running characteristic of centrifugal pump, such as reliability, stability, high efficiency and low vibration, and the stand or fall of its performance depends largely on the internal flow. Generally, when centrifugal pump operates at design flow rate, the distributions of velocity and pressure have universal regulation and the whole flow pattern is very well. Due to the changes of system device, centrifugal pumps are usually used to work at off-design conditions. In most cases, centrifugal pumps are operating at low flow rates. When centrifugal pump operating at low flow rates, it will appear variety of unstable pattern, such as flow separation, backflow and rotating stall. The impeller-volute interaction also was aggravated at low flow rates. It can cause vibration and hydraulic noise. Those phenomena have great influence on the reliability and stability of the pump system.In order to better understand and grasp the internal flow pattern of centrifugal pump running at low flow rates, this paper is aimed to carry out numerical simulation on a low specific speed centrifugal pump for 66 from the perspective of unstable flow. The present numerical simulation is applied with Reynolds-averaged Navier-Stokes equations and RNG k-? turbulent model. The main contents of this paper are as follows:1. The centrifugal pump model has been established by Pro/E. The software ICEM was applied to grid the model. In order to make numerical simulation results more accurate and credible, the grid independence of the model was carried out to decide the number of the grid.2. The steady numerical simulation was executed on centrifugal pump at flow rates 1.0Qd-0.1Qd to get the development process of the backflow at impeller inlet and separation vortex at impeller passages. The backflow zone was obtained by analyzing the circumferential velocity and axial velocity of impeller inlet.3. The unsteady numerical simulation was conducted on centrifugal pump at 1.0Qd, 0.6Qd, 0.3Qd and 0.1Qd. The monitoring points were built on the impeller-volute interface, the circumferential direction of the volute and the section of the volute to analyze the distribution of velocity and pressure by spacing different distance of volute tongue and impeller inlet.4. Points along the circumferential direction of the volute and on the section of the volute were analyzed to obtain the pressure fluctuation characteristic of volute. The effect of volute tongue and the distance of impeller-volute on the pressure fluctuate was discussed. The frequency domain analysis was conducted to get the main driving frequency of pressure fluctuation by the method of FFT.